Three-dimensional (3-D) printing (also known as additive manufacturing or rapid prototyping) allows for the production of three-dimensional objects by building up a material on a layer-by-layer basis. One common 3-D printer employs a printhead extruding material and movable in three Cartesian axes (x,y,z) with respect to a print surface. Under the control of a computer, the printhead moves through a series of positions over the printing surface and at each location deposits a small volume of material to define a portion of the printed object at that location. After a base layer is printed directly on the printing surface, the printhead is successively elevated (z-axis) to print additional layers on top of the base layer and then each succeeding layer until the entire object is printed.
As an example, U.S. Pat. No. 8,644,964 describes an excavator that includes an upper frame pivotally mounted to an undercarriage. The excavator also includes a large boom that extends from an upper frame adjacent to a cab. The boom is rotatable about a vertical arc by actuation of a pair of boom cylinders. A dipper stick or arm is rotatably mounted at one end of the boom and its position is controlled by a cylinder. The dipper stick or arm is mounted to an end effector in the form of a printhead that is pivotable relative to the arm by means of a cylinder. This method limits the height of any structure constructed, to the reach of the combined boom and dipper stick. Additionally, every time the print head is to be moved, the boom angle must be adjusted in conjunction with the dipper stick angle being adjusted, as well as the rotation of the machine being adjusted.
Fabrication of precision linear ways and the drive mechanism associated with the ways can be costly or difficult, particularly for large systems. Further the fabrication process is normally slow, limited by a speed at which a single carriage holding one or more printheads can be maneuvered within a framework of the ways.